He was considered both times, but what if Nixon said yes? Then we have a POTUS Bush in the 1970's, possibly a two-termer depending on the W.
Your Majesty, this assumes Bush defeats Yarborough in '64 or '70, and the OTL margins are easy to butterfly.
Even with a 1968 POD, LBJ won't lead the ticket.
Oops, got confused. But if LBJ's resignation letter of 1964 (which Bird intercepted) is *smuggled out* and published, then liberals and Southerners headdesk in unison. Now that's a TL.